In this project reactive water soluble macromolecules have been synthesized and their effects on mammalian cells in culture studied, the main emphasis being on the interaction of the macromolecules with cell membrane. Dextran, a natural polysaccharide, is biologically inert - it is neither bound nor consumed by cells; to this compound were attached highly reactive groups and the effects of these derivatives on mouse cells growing in culture were studied. The following were used as reactive groups: (a) mercury (II) compounds, which bind very strongly to sulfhydryl groups; (b) diazonium compounds, which react with tyrosine and histidine residues of proteins; (c) organic dyes, which bind nucleic acids; (d) the organic dye, Rose Bengal, which in the presence of light turns oxygen from the normal, inert triplet state into the very short-lived and extremely toxic singlet state. The substituted dextrans (a)-(c) represent reagents which bind strongly and selectively to some components of the surface of the living cell; the last compound (d) in the presence of light transforms oxygen so that it destroys the binding site of th compound. BIBLIOGRAPHIC REFERENCES: Blob, L. N. Vengris, V. E., Pitha, P. M. Pitha, J.: Uptake and fate of water-soluble, nondegradable polymers with antiviral activity in cells and animals. J. Med. Chem. 20: 356-359, 1977. PItha, J.: Polymeric analogs of nucleic acids. Polymer 18, 425-430, 1977.